This invention relates to an engine control device for controlling an engine and, more particularly to an engine control device suitable for controlling an engine provided with a fuel injection device for injecting fuel.
With the widespread of fuel injection devices called injector in recent years, control of fuel injection timing and fuel injection amount, namely, the air-fuel ratio has become easy, which makes it possible to improve engine output and fuel consumption and to clean exhaust gas. As to the fuel injection timing, it is common that a phase state of a camshaft, a state of an intake valve, to be exact, is detected, and, based on the detected result, fuel is injected. However, a cam sensor for detecting the phase state of the camshaft, which is expensive and increases the size of a cylinder head, is difficult to employ in motorcycles or the like, in particular. To solve this problem, an engine control device adapted to detect a phase state of a crankshaft and an intake pipe pressure and, based on those, to detect a stroke state of a cylinder is proposed in JP-A-H10-227252. With this prior art, it is possible to detect a stroke state of a cylinder without detecting a phase of a camshaft, so that it is possible to control fuel injection timing based on the stroke state.
To inject fuel from a fuel injection device as mentioned above, the fuel in the fuel tank must be pressurized by a fuel pump before supplied to the fuel injection device. As is well known, since the pressure of the fuel pressurized by the pump fluctuates, a pressure control valve called regulator is used to provide an upper limit on the fuel pressure. In the case of a motorcycle, the regulator is generally provided in the close vicinity of the fuel injection device and is usually so constituted that a prescribed regulator control pressure usually set by a spring or the like is added to the fuel on top of a pressure of an atmosphere into which the fuel is injected by the fuel injection device, for example, a pressure in an intake pipe, as a back pressure. Thus, the fuel injection pressure, which is a difference between the pressure of the fuel supplied to the fuel injection device and the pressure of the atmosphere into which the fuel is injected, is always equivalent to the regulator control pressure of the regulator.
However, when the regulator is provided in the close vicinity of the fuel injection device, a return line for returning surplus fuel from the regulator to the fuel tank must be provided for each fuel injection device. Also, in most cases, the regulator is manufactured by the same manufacturer of the pump but, when the pump and the regulator are disposed separately, they are supplied separately. This increased the number of parts and makes cost reduction by making parts into assemblies impossible. Then, it can be thought to place the regulator in the vicinity of the pump by, for example, making the pump and the regulator into an assembly. This constitution not only makes the return line unnecessary but also makes it possible to reduce the number of parts and the costs.
However, in the event that the regulator is disposed on the pump side as has been described above, since the back pressure of the regulator is constituted by the atmospheric pressure, where the atmospheric pressure changes as the altitude changes, the fuel pressure also changes. There has been proposed a fuel injection control method which is described, for example, in JPA-A-S61-178526 as a method for compensating for a change in fuel pressure caused when the atmospheric pressure fluctuates. In this fuel injection control method, an atmospheric pressure is detected by an atmospheric pressure sensor, whereby the fuel injection amount is corrected based, for example, on a ratio between a reference atmospheric pressure and an atmospheric pressure so detected. According to this method, while the fuel injection amount can be compensated irrespective of the fluctuation of atmospheric pressure, the atmospheric pressure sensor is needed, and the number of components is increased by the additional of such a component, this leading to an increase in production costs.
When the regulator is placed in the vicinity of the pump, the back pressure of the regulator must be ambient pressure, so that the pressure of the fuel supplied to the fuel injection device is generally constant (When the ambient pressure changes with altitude, for example, the fuel pressure is also changed.). On the other hand, when no surge tank is provide in the intake pipe as in the case of motorcycles, the pressure in the intake pipe into which the fuel is injected, namely the pressure of the atmosphere into which the fuel is injected is changeable. This means that the injection fuel pressure, which is the difference between the pressure of the fuel supplied to the fuel injection device and the pressure of the atmosphere into which the fuel is injected, is unstable. When the injection fuel pressure is unstable, the amount of fuel injected from the injection device per a unit time becomes unstable. This makes it impossible to obtain a fuel injection amount to attain a desired air-fuel ratio only by controlling the fuel injection time.
As a device for correcting the fuel injection amount based on an injection fuel pressure, there is an engine control device disclosed in JA-A-H08-326581. The engine control device detects an injection fuel pressure, integrates it over a given period of time to obtain the area thereof, compares the area with reference area values, and corrects the fuel injection amount based on the comparison result. In this engine control device, however, the infection fuel pressure must be integrated, so that the operation load is unavoidably large. Also, since the reference values with which the integral value of the injection fuel pressure is compared must be organized into a map for every operation state of the engine and stored, a memory with a large capacity is needed. Naturally, the operation load in withdrawing the maps and making the comparison is large.
The invention was made with a view to resolving the problems and an object thereof is to provide a control device for a four-stroke engine which can accurately control the fuel injection amount and time at a transitional time while reducing an operational load related to the control of fuel injection and which can attempt to reduce the number of components and production costs.
According to a first aspect of the Invention, there is proposed a control device for a four-stroke engine having an intake valve between a combustion chamber and an intake port and having at least one intake control valve for one intake port of the combustion chamber, the control device comprising a pump for pressurizing a fuel in a fuel tank, a regulator opened to an atmospheric pressure for regulating an upper limit value for the fuel pressurized by the pump, a fuel injection device for injecting the fuel regulated an upper limit value thereof by the regulator into the intake port, intake pressure detecting unit for detecting an intake pressure between the intake control valve and the combustion chamber, at least either atmospheric pressure detecting unit for detecting an atmospheric pressure or pump delivery pressure detecting unit for detecting the pressure of the fuel pressurized by the pump, and fuel injection control unit for controlling the fuel injection device based on at least either of an atmospheric pressure detected by the atmospheric pressure detecting unit and a fuel pressure detected by the pump delivery pressure detecting unit and an intake pressure detected by the intake pressure detecting unit, wherein the intake pressure detecting unit detects an intake pressure a plurality of times while the four-stroke engine completes four strokes of intake stroke, compression stroke, expansion stroke and exhaust stoke, and the fuel injection control unit calculates a fuel injection time based on at least one of a plurality of intake pressure values detected by the intake pressure detecting unit so as to inject the fuel with an injection initiating timing according to the fuel injection time so calculated.
According to a second aspect of the invention, there is proposed a control device for a four-stroke engine as set forth in the first aspect of the invention, wherein the pump and the regulator are disposed within the fuel tank.
According to a third aspect of the invention, there is proposed a control device for a four-stroke engine as set forth in the first or second aspect of the invention, wherein the intake pressure detecting unit detects the intake pressure at least when a fuel injection time calculated by the fuel injection control unit is over or is about to be over.
According to a fourth aspect of the invention, there is proposed a control device for a four-stroke engine as set forth in any of the first to third aspects of the invention, wherein only the pump delivery pressure detecting unit is provided.
According to a fifth aspect of the invention, there is proposed a control device for a four-stroke engine as set forth in any of the first to third aspects of the invention, wherein only the atmospheric pressure detecting unit is provided.
According to a sixth aspect of the invention, there is proposed a control device for a four-stroke engine as set forth in any of the first to third aspects, or the fifth aspect of the invention, wherein the atmospheric pressure detecting unit detects an atmospheric pressure from an intake pressure detected by the intake pressure detecting unit.
According to a seventh aspect of the invention, there is proposed a control device for a four-stroke engine as set forth in any of the first to third aspects, or in the fifth or sixth aspect of the invention, wherein the intake pressure detecting unit detects at least an intake pressure resulting immediately before the intake valve opens.
According to an eighth aspect of the invention, there is proposed a method for controlling a four-stroke engine having an intake valve between a combustion chamber and an intake port and having at least one intake control valve for one intake port of the combustion chamber, the method comprising the steps of pressurizing a fuel in a fuel tank, regulating by a regulator opened to an atmospheric pressure an upper limit value for the fuel pressurized by the pump, injecting the fuel regulated an upper limit value thereof by the regulator into the intake port, detecting an intake pressure between the intake control valve and the combustion chamber, performing at least either the step of detecting an atmospheric pressure or the step of detecting the pressure of the fuel so pressurized, and controlling the fuel injection based on at least either an atmospheric pressure detected through the step of detecting an atmospheric pressure or a fuel pressure detected through the step of detecting a fuel pressure and an intake pressure detected through the step of detecting an intake pressure, wherein in the step of detecting an intake pressure, an intake pressure is detected a plurality of times while the four-stroke engine completes four strokes of intake stroke, compression stroke, expansion stroke and exhaust stoke, and in the step of controlling the fuel injection, a fuel injection time is calculated based on at least one of a plurality of intake pressure values detected through the step of detecting an intake pressure so that the fuel is injected with an injection initiating timing according to the fuel injection time so calculated.